The present invention relates to a method and apparatus for automated testing of relays and more particularly to automatically ascertaining which terminals of the relay are connected to a relay coil and which terminals of the relay are connected to the relay contacts, and then to automatically testing and reporting the functional parameters of the relay.
The need to test the operating parameters of relays has been around almost since the invention of the telegraph. Traditionally, relay function parameters have been tested by skilled electrical technicians who understood the construction and operation of the relay coils, armatures, and solid metallic contacts.
However, in recent years electronic and electromechanical controls have invaded many predominately mechanical product fields. For example, many modern automobiles contain at least half a dozen microprocessors to control a large variety of hitherto purely mechanical processes.
Automobiles are still basically low-voltage products, operating primarily at twelve volts DC (12VDC). Therefore, supplying even a modest amount of power at that low voltage can involve switching a substantial magnitude of electrical current. However, control of some of these processes requires operating power far in excess than that which can be supplied directly at the output of a microprocessor. Also, many of those high-power processes can produce a substantial inductive xe2x80x9ckickxe2x80x9d when electrical power is removed from them. Therefore, a more-or-less convention relay with a coil and solid metallic contacts is the only economically-viable solution.
However, like the automobile, many kinds of traditionally mechanical equipment are still repaired and maintained by mechanical craftsmen with little appreciation of the nicities of electromechanical devices or time to perform careful manual tests of such devices. Also, when performing a mechanical repair involving an element of electromechanical control, there may be temptation to replace relays rather than take the time to perform careful tests of them by manual means. This is especially true with the increasing use of plug-in mounting of relays, which requires no unsoldering or other time-intensive disassembly in order to remove the relay.
In recent years electronic devices have been designed and manufactured to perform the traditional functions of relays. These are often even more tedious to test manually.
Therefore, it is an object of the present invention to enable a mechanic, unskilled in the intricacies of relay construction and operation, to test a relay easily and quickly. To that end, a mechanic wishing to test the functional parameters of a relay should not have to use a volt-ohm meter (VOM) to ascertain which of the relay""s terminals are connected to the electromagnetic coil that operates the armature of the relay. Also, the mechanic should not have to use a VOM in order to determine the presence and polarity of any coil-suppression diode or resistance network that might be connected across the coil terminals of the relay. Also, a VOM should not have to be used to ascertain if the relay contacts are normally closed (NC), normally open (NO), or single pole, double throw (SPDT)
According to one aspect of the present invention, a program-controlled microprocessor ascertains the impedance between each terminal of the relay and every other terminal of the relay. In this way, the microprocessor determines which are the coil terminals, which are the contact terminals, and the de-energized condition of the contacts. The microprocessor also determines whether or not there is a coil-suppressor diode or resistance network and the polarity of a diode, if present, and if the diode is in good condition. The microprocessor then applies current to the relay coil, in the proper polarity, and examines the action and condition of the contacts. The microprocessor then indicates to the operator the condition of the various parts of the relay, as ascertained in the test.
The various objects, features, and advantages of the present invention will be readily apparent from the following specification and drawings.